"The MK39 was essentially an improved MK15 with a drogue parachute
system for surface-burst capability against hardened targets. It was
intended to be a lighter, higher-yield MK15 with a new boosted primary.
……… The MK39 Mod 0 was design-released by Sandia in April 1956,
and a prototype MK 39 was fired during Operation REDWING later in the
summer. ……………………. Initial units of the MK39, described
as an "improved, lightweight version of the Class C thermonuclear
bomb," were produced in February 1957. On November 18, 1957, the
Air Force notified the DMA that SAC had an urgent military requirement
for a low-altitude deliverable "laydown" MK39 bomb. Early in
March 1958, the MLC requested the AEC to develop an advanced "laydown"
design; this project was assigned to LASL and became the MK39-Y1 Mod2
bomb. Wind tunnel tests of the MK39-Y1 Mod 2 were completed by October
1958. …………..

The "laydown" MK39 was dubbed the "Lone Star"
project; the bomb was encased in a large semi-rectangular
"boat" lined on its bottom with aluminum honeycomb to absorb
impact. The whole assembly weighed 7,500 lbs. and was slowed to a ground
impact speed of 30 feet per second by a 130-foot diameter parachute (the
largest ever fabricated at that time). The "Lone Star" was to
be dropped from an altitude of 1,000 feet by B-47 or B-52 bombers. The
project was canceled when it was superseded by MK28 and MK43 "laydown"
weapons. Approximately 700 MK39s in Mods0, 1, and 2 were manufactured
between February 1957 and March 1959; all were retired between January
1962 and November 1966. …………………………..

The MK39 was designed to be very safe, reliable, and simple. It could be
readied for combat quickly and the weapon case was sealed to simplify
storage. Like several mods of the MK15, the MK39 featured an
impact-absorbing aluminum-honeycomb "false nose" forward of
the warhead's "physics package." The "false nose"
was tipped with a contact fuse consisting of two aluminum plates
separated by an air space. The MK39 casing weighed 6,000 lbs.;
fully-loaded bomb weight was between 9,000 and 10,000 lbs. The bomb
centerbody measured 34.5" in diameter; the aft parachute section
was 42" in diameter. Overall length was 11' 7"; the tail fins
spanned 55". The bomb was built in two separate yields (Y1 and
Y2)." *